Low-cost, simultaneous, single-sequence genotyping of the HLA-A, HLA-B and HLA-C loci.

ABSTRACT

New automated DNA sequencing technology has enabled the development of an assay for genotyping the three major HLA class 1 loci from a single sequence of each gene containing exon 3, intron 2 and exon 2. The assay allows 31 subjects (with 3 negative controls) to be genotyped at all three loci simultaneously, using a 96-well plate format. Genotypes were assigned by comparing each sequence to a database of 307 HLA-A, 563 HLA-B and 166 HLA-C alleles. Unequivocal, 4-digit allele assignments were made for 40 of 130 HLA-A genes, 82 of 130 HLA-B genes and 97 of 130 HLA-C genes from 21 European, 20 Tongan and 24 Niuean subjects. Ambiguity in interpretation of the sequence contributed to 66 of the 170 equivocal allele assignments, and 105 equivocal assignments were due to polymorphisms outside exons 2 and 3. All known alternative interpretations of ambiguous genotypes were identified, and seven HLA-B and two HLA-C ambiguities were resolved by reading the out-of-phase exon 2 sequence that followed an indel in intron 2. The genotypes of a subgroup of 27 heterozygous subjects, whose genotypes contained all of the alleles identified in this study, were confirmed with commercial, generic PCR-SSP typing. In European subjects, the repertoire of HLA-B/HLA-C haplotypes was almost identical to previously published data. We identified five new HLA-B/HLA-C haplotypes in the Polynesian subjects, and the remaining haplotypes were of Asian origin. In summary, we are describing a low-cost, sequencing assay for the three major HLA class I loci that provides a level of resolution that is comparable with a commercial PCR-SSP assay.